In general, a pickup is a coil of conductive wire wrapped around or glued to a permanent magnet. Nearby vibrating metal strings induce an alternating current at the frequency of vibration.
Prior to the embodiments of the present invention, there were only non-removable magnets in guitar pickups, meaning that the pickup only got the tonal characteristics of one type of magnet, and if a guitarist wanted a different tone, they would need to buy a different pickup all together, an expensive endeavor, or to take apart the pickup and force the magnet out, which is dangerous, difficult, voids the warranty of many pickups, and can only be done a finite number of times before the screws get stripped or the bobbins get over-drilled and structural integrity is compromised. In most types of pickups, it is desirable to keep magnets in place to avoid distortions in sound.
There are three types of standard pickups widely sold, the humbucker, single coil, and p90. A normal, standard humbucking guitar pickup has the following major components: a baseplate, a magnet, two coils, and 12 pole pieces, six on each coil. The coils are suspended over the baseplate by friction between the pole pieces, leaving a cavity between the two rows of pole pieces. This is where the bar magnet is glued or otherwise fixed in the pickup.
A normal, industry standard P90 has the following major components: two plastic/fiber bobbins, a wooden spacer, a metal spacer, a solid metal baseplate, and six pole pieces/screws (both to keep the pickup together and to conduct magnetic current). The bobbins are separated by the wooden spacer vertically, and around the spacer is wrapped the wire coil. The bottom bobbin (now connected to the completed coil) is then placed on top of the metal spacer, which is then placed on top of the baseplate. The magnets are epoxied on either side of the spacer, and the pickup is screwed together.
The single coil pickup is normally composed of these major parts: two magnets, two bobbins, a wooden spacer, and six pole pieces. The bobbins are placed on either side of the wooden spacer, and the coil is wrapped around the wooden spacer and in between the bobbins, creating the coil. Pole pieces are inserted through the bobbins and spacer and out the other end, sticking out a bit. Magnets are epoxied on either side of the part of the pole pieces that sticks out of the framework.